The Dutch national media service also dealt with this question. The head of the Dutch military intelligence service (who conducted the operation against the Russians) says it's standard for them to conduct operations in that way.
More specifically, he is quoted saying the following (in Dutch):
Ik zou het terugkijkend nog steeds niet anders doen omdat mijn inlichtingenoperaties in dit geval gewoon voorgaan. Als ik ze vast had gezet dan had ik het misschien niet kunnen uitvoeren zoals ik het nu heb kunnen doen.
Roughly translated to English:
Looking back, I wouldn't do anything different because my intelligence operations are more important. If I had detained them then I may not have been able to conduct those in the way I have now.
Having read the quote a few times, it is a bit unclear what the part in bold refers back to. My best guess is that it refers back to the intelligence operations. Assuming that is the case, the answer to your question is that it may harm on-going or future operations.
The article also provides some other considerations given by an external lawyer, however, those are not named explicitly by the Dutch security service. Those considerations include the precarious relationship with the Russians (with reference to the downing of MH17) and their diplomatic status.